In a typical prior art magnetic disk recording system a slider containing magnetic transducers for reading and writing magnetic transitions is urged toward the rotating disk by a suspension. An air-bearing develops under the slider and causes it to fly. The term “fly-height” and air-bearing height will be used interchangeably herein.
A slider fly-height of less than 10 nm is required for areal densities of 60 Gb/in2 and greater. To reach the 1 Tb/in2 mark, fly-heights in the 2-3 nm range are needed. Accordingly, it is becoming increasingly difficult to measure the actual fly-height of sliders. The most common technique using white light interferometry works adequately for a fly-height above 10 nm, but it looses accuracy below 10 nm. In addition, it is very sensitive to the optical constants of the slider overcoat. Another technique uses small solid bumps of known height on the disk and measures the acoustic emissions as the slider passes over or hits the bumps. Since it is impractical to make bumps below 5 nm in height, this particular technique looses accuracy for very small fly-heights.
In published U.S. patent application 20030067698 (Apr. 10, 2003) by Dakroub, et al. a method is described for measuring the fly-height of a slider using a fixed source write signal applied to an inductive element of the write head, generating a magnetic field with a stray magnetic field portion. A magnetoresistive element of the read head coupled with the magnetic field produces an initial field strength signal. As the disk rotates, the slider flies above the disk decreasing the density of the stray magnetic field portion, thereby, decreasing the amplitude of the field strength signal. The decreasing amplitude of the field strength signal is calibrated to a predetermined operating fly-height profile to correlate fly-height of the slider to the decreasing amplitude of the field strength field.
A method for measuring the fly-height of a slider using a thermal source and a thermal detector is described in published U.S. patent application 20030058559 (Mar. 27, 2003) by Brand, et al.
A laser diode generates light which is reflected off of the disk to a semiconductor laser light detector in the system described in published U.S. patent application 20030007279 (Jan. 9, 2003) by Johnson, et al.
In published U.S. patent application 20020176185 (Nov. 28, 2002) Fayeulle, et al., a method for measuring the fly-height of a slider using a disk with radial grooves in the surface is described. As the disk rotates, the radial grooves pass under the slider and induce a perturbation in the signal. By measuring the perturbations in the signal caused by the grooves in the disk surface, and by processing the measurement signal, a vertical spacing signal proportional to the vertical spacing between the disk and the head can be obtained.
In published U.S. patent application 20020071196 (Jun. 13, 2002) by Chapin, et al., the fly-height detector apparatus comprises a receiver circuit for measuring the frequency of the read/write head; a means perturbing the gap between the read/write head and the data storage surface to invoke a dynamic response in the read/write head; and a processor circuit responsive to the receiver circuit to derive a fly-height in relation to the dynamic response frequency. The processor circuit comprises a memory in which is stored a numerical model describing a functional interrelationship between the fly-height and the read/write head frequency.
In published U.S. patent application 20020097517 (Jul. 25, 2002) by Bonin, et al., a slider is described with a field emission sensor that senses fly-height. The sensor has an electrode tip disposed on the slider. The electrode tip faces a media surface across a gap. The sensor conducts a tunneling current through the gap and provides an output representing the length of the gap.
Published U.S. patent application 20020001151 Jan. 3, 2002 by, J. H. Lake describes a system for measuring fly-height of a slider over a rotatable magnetic disk. The system determines the fly-height of the slider based on the measured pulse width and amplitude of the read back signal.
In published U.S. patent application 20010035960 (Nov. 1, 2001) by M. M. Johnston a method is presented of fly-height testing using a light emitting diode which generates a light that is reflected off the medium and the slider. The reflected light is directed to detectors capable of generating an electrical signal based on the amplitude of at least one wavelength of light in the reflected light. A distance calculator then determines the distance from the slider to the medium based on the electrical signal.